This invention relates to an improved carburetor to be mounted on a two-cycle engine to provide a power source for chain saws, trimmers and weed cutters and the like.
It is an object to provide a carburetor with a suction priming system which can draw fuel into the diaphragm control chamber prior to starting or following a fuel runout.
It is a further object to provide a carburetor as described which can be used on chain saws, trimmers, weed cutters and the like so designed that it can operate in upright or other positions such as upside down and side positions--in other words, an all-position carburetor. For this reason, the carburetor is designed with a pressure chamber mechanism to insure that the pressurized fuel flow from the pump to the fuel jets is accurately controlled regardless of the carburetor positions, this being done in connection with a pulse link between the engine and the diaphragm chamber.
Diaphragm carburetors in general have a diaphragm chamber which opens to the main jet and the idling jet orifices, there being a diaphragm in the diaphragm chamber which controls a fuel inlet valve which is interposed between a pulse fuel pump and the diaphragm chamber.
In the operating phase of the engine, the diaphragm continually opens and closes the inlet needle so that fuel can enter the diaphragm chamber in response to suction pulses of the engine. The pressure pulse is being isolated from the diaphragm chamber by check valves. Accordingly, a certain amount of fuel can be maintained in the diaphragm chamber at a fixed pressure, and the fuel then flows from the diaphragm chamber to the fuel jet orifices depending on the position of a throttle valve. As previously pointed out, where insufficient fuel is maintained in the chamber during the starting phase, for example, in a cold climate or trying to restart an engine which has run out of fuel, it is important to refill the fuel in the diaphragm chamber.
It is, therefore, an object of the present invention to provide a primer system which can be actuated manually prior to the starting or restarting of the engine to create a suction, that is, a sub-atmospheric pressure, in the diaphragm chamber and cause the resulting motion of the diaphragm to open the fuel valve and cause fuel to flow into the diaphragm chamber for starting purposes. After the engine is started, the pressure pump will function to provide the fuel supply and the manual suction system will be automatically cut out. Nevertheless, when the engine is not running, there is no suction applied to the diaphragm chamber and the inlet needle remains in its closed position and it will remain so until the engine is started or until the manual priming system is actuated. The primer can also be used to remove excessive fuel from the diaphragm chamber should this be desirable. Suitable check valves are provided in the primer system to achieve the required sub-atmospheric pressure to accomplish this.
It is, therefore, an object to provide a relatively simple construction in a carburetor to accomplish the above objects in connection with the fuel supply and the priming system.
As explained above, by providing the manually operated suction priming system, it is no longer necessary to actuate the diaphragm manually from the outside of the carburetor. The fuel inlet valve in the form of a needle valve which works in conjunction with linkage attached to the diaphragm is moved by resilient spring pressure acting on the linkage to close in the direction of the fuel inlet flow. In addition, it is noteworthy that the fuel can be sucked into the diaphragm chamber when the fuel supply pump is not operating. As an illustration of a carburetor designed to perform the above-described objects, a detailed explanation is provided in connection with the single drawing.